I'm not familiar with the polys listed how about comparisons with Competition and X1. Thanks!
Power
Competition is lowest powered of the strings between the 3. You can take a pretty good whack at the ball and still hold it down. I found that for my game, Competition was too low powered and with less feel at net. My serve seemed to suffer a bit as well. Good string for a big hitter though, I do hit fairly hard, but not enough for this string to be effective.
X1 was a string that I really wanted to like. It feels cool and I had the red color which looked pretty sweet. In the end though, it just felt dead to me. I never adjusted to the sting and couldn't read the power level at all. It seems fairly close with the new IsoPro in terms of power, but I didn't get the consistency.
IsoPro is a farily powerful string. It's close to PSGM in that regard. It just pockets the ball very well which allows me to have slightly better control and feel.
Greatest to least: IsoPro>X1>Competition
Control
Competition is a pretty solid control string. Most folks would agree that polys in general make a solid choice for players looking for maximum control and Competition is no exception. The sacrifice in most cases is usually power.
X1 as mentioned above was all over the board with me. Just when I hit a few good shots and thought I was getting a feel for the string, I would get what seemed an inconsistent response. I'm guessing I have not increased my tension as much as I should have. I have heard only great things about this string in general so it surprised me.
Control is not IsoPro's best attribute, but it has a very consistent response so it was easy for me to "dial in" and adjust. Deep ball pocketing, similar to what gut must play like (I've never played with gut). It wasn't as elastic as X1 on the stringer and I think that helped with the response consistency.
Competition>IsoPro>X1
Spin
Of the 3 strings, Competition was able to impart the most spin as you might expect. You have to take a more aggressive cut at the ball and the way a string moves on the poly bed (rebound effect of the string returning to it's position) gave Competition an advantage here. IsoPro does not do a bad job imparting spin though. I find that shots like a slice backhand actually benefit from the playability of the IsoPro strings and have a nicer spin effect. With X1 my woes continued. I just could not dial in topspin shots, but spin serves did well.
Competition>IsoPro>X1
Sting movement
Competition moves the least, again a common desireable property of a poly. I was pleasantly surprised by IsoPro though. They did not move nearly as much as I thought they would - much less than syn guts or other multi's that I've tried. For the first couple hours they didn't really move at all. I've also noticed that they don't appear to notch like syn guts and multi's can. IsoPro is very much a unique string in construction and it shows. X1 moved quite a bit, though I personally don't mind that much because straightening my strings allows me to focus between points.
Most movement to least movement:
X1>IsoPro>Competition
Comfort
This is a "no-brainer" for me. IsoPro is hands-down the most comfortable string among the three. I probably would have felt better with X1 had I not been trying so hard to generate spin and overcoming the dead feeling I got. Competition is somewhat soft for a poly, but still much more harsh on the arm than the others.
Most comfortable to least comfortable:
IsoPro>X1>Competition
Durability
I can't comment much on this because I'm not a string breaker. I tend to cut strings out long before I'd ever break them. From a tension holding standpoint, IsoPro seems to be holding up well. I have 2 frames strung with them and after the first 5-6 hours of hitting on each, they are holding up well. The X1 seems to offer much less in this area. I think that Competition is very durable, but may not maintain playability which is typical of polys.
You didn't ask for feel/playability, but I really like IsoPro in that area. The pocketing effect when hitting the ball gives me confidence. It's a very personal thing and everyone has different definitions of feel, but I really like IsoPro.
Overall, I've been very pleasantly surprised by IsoPro. I would recommend stringing at the lower part of the range for your frame, that is where it really shines. I don't have any affiliation with Isospeed, but after trying so many strings over the last 5 months, I was begining to think that I would just have to settle for something and get used to it.
You may also want to check out the online playtest at:
http://www.racquetsportsindustry.com/articles/2007/06/isospeed_professional_17.html
Hope this helps.